1. Technical Field
This invention relates generally to auxiliary methods and apparatus for starting internal combustion engines. More particularly, the invention relates to a method and apparatus for starting such engines which adapts to the intake requirements of a low-compression-ratio compression ignition engine.
2. History of Related Art
Starting internal combustion engines of the compression ignition type is generally accomplished by means of a cranking motor, the main shaft of which is coupled to the engine crankshaft by an automatic clutch. The cranking motor is typically an electric or compressed air motor. In some cases, however, the added weight and/or complexity of a cranking motor may not be tolerable. Extra weight is especially critical for Unmanned Aerial Vehicles (UAVs), which make use of small, lightweight primary engines. If a diesel engine is used in such an application, it is usually of the low-compression type (to save weight), which runs well when warm, but is notoriously hard to start.
It is known to eliminate the disadvantages of the conventional starting device by connecting a direct current motor to an air motor in the same axial line, with an air pressure source obtained using a compressor driven by the engine, such as a supercharger. However, this solution also does not address those applications which do not tolerate the weight of a compressor in addition to that of the engine.
When mechanical complexity or weight is a consideration, it is also known to use external, auxiliary internal combustion engines for starting purposes. Such methods typically involve an auxiliary motor connected in some mechanical fashion to the primary motor during starting operations, perhaps using a transmission. While this method may be highly inconvenient in most instances, such as for diesel trucks, it is useful in those cases which lend themselves to the use of auxiliary, or offboard equipment for starting operations. It is also known to introduce exhaust gases from an auxiliary engine, via heat exchanger, into the induction system of the primary engine. However, such methods still fail to completely address the difficulty of starting a low-compression engine, which may demand extra fresh air, or suffer from over-pressure due to excess exhaust gas.
Therefore, what is needed, is a method and apparatus suited to starting a lightweight, low-compression, internal combustion engine. The method and apparatus should make use of conventional components wherever possible, and should be inexpensive. The method and apparatus should adapt to the need for extra fresh air, or less exhaust volume/pressure from an auxiliary engine. Finally, the method and apparatus should add little, if any, weight and mechanical complexity to existing low-compression engines used in weight-sensitive applications, such as for UAVs.
The invention includes a method for starting a primary engine using the exhaust gas stream from an auxiliary engine, which is usually a diesel engine. The method includes the steps of conducting the exhaust gas stream from the auxiliary engine to the air induction system of the primary engine, adding fresh air to the exhaust stream, and reducing the pressure of the exhaust stream before it arrives at the air induction system.
Conducting the exhaust stream from the auxiliary engine to the air induction system of the primary engine is typically accomplished using a conduit, such as an exhaust manifold, or some other system of piping. Adding fresh air and reducing the pressure of the exhaust stream before the exhaust gas stream arrives at the air induction system is typically accomplished using a check valve in line with the conduit. The pressure of the exhaust stream is typically reduced by diverting a portion of the exhaust stream away from the air induction system. Thus, the check valve typically has an inlet in fluid communication with the fresh air, and an outlet for diverting a portion of the exhaust stream away from the air induction system. The method may also include the steps of starting the auxiliary engine and idling the auxiliary engine, to enhance the oxygen content of the stream, and increase the presence of active radical species that may enhance ignition for the primary engine.
The invention also includes an apparatus for starting a primary engine using the exhaust gas stream from an auxiliary engine, which includes a means for conducting the exhaust gas stream from the auxiliary engine to the air induction system of the primary engine, a means for adding fresh air to the exhaust gas stream before the stream arrives at the induction system, and the means for reducing the exhaust gas stream pressure to prevent back pressuring of the exhaust system of the auxiliary engine.
The means for conducting the exhaust gas stream from the auxiliary engine to the air induction system is typically a conduit, such as a system of piping, or manifolds. The means for adding fresh air to the exhaust gas stream, as well as the means for reducing the exhaust stream pressure, is typically a check valve.
The invention also includes a system for starting a primary engine which includes an auxiliary engine and the conduit. The conduit is in fluid communication with the exhaust gas stream of the auxiliary engine and the air induction system of the primary engine. The system also includes a check valve in fluid communication with the conduit.
Preferably, the auxiliary engine is a diesel engine. The check valve operates to admit fresh air and the exhaust stream, and to divert a portion of the exhaust stream away from the air induction system. As mentioned above, the exhaust stream typically includes active radical species, and has an idling oxygen content which is greater than the operating oxygen content.